Method of fastening objects to hard material



June H3, 1967 M. HILTI METHOD OF FASTENING OBJECTS TO HARD MATERIAL Original Filed April 18, 1963 2 Sheets-Sheet l INVENTOR June 13 1967 M. HlLTl 3,324,542

METHOD OF FASTENING OBJECTS TO HARD MATERIAL Original Filed April 18, 1963 2 Sheets-Sheet 2 eoo-- 5 O I 2 3 4 5 G 7 0 angle INVENTOR 3,324,542 METHOD F FASTENING (IIlBJECTS T0 HARD MATERIAL Martin li-lilti, Vaduz. Liechten tein, assignor to Anstalt i'iir Montage-Technik, Vaduz, Liechten tein Continuat on of application Ser. No. 271,520, Apr. 18, 1963. This application Dec. 18. 1964, Ser. No. 422,064 1 Claim. (Cl. 29-432) This is a continuation of application Ser. No. 271,520, filed Apr. 8, 1963 now abandoned. This invention relates to methods and apparatus for securing any of a variety of objects, such as wiring conduits and the like, to hard structural materials, especially concrete, cement, and the like. More in particular, this invention relates to improvements in the technique of driving anchoring studs into hard materials by means of hammer blows applied by a hand-held driving tool.

During construction work, it frequently is necessary to attach hangers such as wall hooks, binding, clips, etc., to hard material of the type basically comprising concrete or cement. Various approaches have been developed in the past for solving this problem .For example, recesses were chiseled out of the hard material and plugged with relatively soft material suitable for supporting the hangers by conventional means. It also is known to drive fasteners, such as studs, directly into the hard material, as by shooting the stud into the hard material at high velocity from a gun-type tool. Tools also now are available for driving studs by the hammer-like blows of a piston member, for example as shown in my US. Patent 2,896,209, issued on July 28, 1959. Such tools also can be provided with means for intensifying the hammer impact against the stud by the use of an explosive cartridge, e.g. as shown in my copending application Ser. No. 795,819, filed Feb. 26, 1959, now Patent No. 3,129,429, issued on Apr. 21, 1964.

Conventional anchoring techniques did not provide a fully satisfactory solution to the problem of fastening to certain hard materials, particularly concrete and cement. For example, when the usual stud (i.e. having a cylindrical shank with .a pointed tip at one end and a head at the other end) is driven into concrete, it typically is found that the stud will have insufficient holding power. That is, the stud can be pulled out from the hard material with a relatively light force.

In accordance with the approach disclosed herein, however, it has been found that this lack of holding power can be alleviated significantly by means of an improved fastening method wherein a stud having a slightly noncylindrical shank, i.e. formed with a very small taper angle, is driven into the hard material by means of a hand-held tool which is provided with a piston-like member having centering surfaces adapted to cooperate with mating centering surfaces on the head end of the stud. Through use of this technique, the holding power of the fastening device will be substantially increased over conventional methods, apparently because hard material such as concrete is so friable that it tends to crumble excessively around the shank of the stud in the conventional fastening systems, Whereas in the present invention such crumbling apparently is minimized by the slight taper angle of the stud shank, aided by a relatively low speed of penetration together with accurate guiding during the driving operation.

It is recognized that studs and bolts used heretofore have been provided with tapered shanks, e.g. as shown in US. Patent 2,166,041, issued to Cox on July 11, 1939. Such studs were not tapered to provide improved holding power in hard materials such as cement and concrete, and the taper angle typically used with such prior studs was substantially larger than the angles found to be useful for the purposes of the present invention, e.g. the

3,324,542 Patented June 13, 1967 above-mentioned Cox patent shows an included taper angle (i.e. as measured from one side of the stud to the opposite side) of about 7 as compared to the optimum included taper angle of about 1.5 in the present invention. It may further be noted that the tapered studs as shown in the Cox patent were designed to be shot into tough non-crumbling material such as steel, and when such studs had completed penetration, it was possible for the stud to be so deformed as to reduce the taper angle. However, once such a stud had penetrated the work material, it lost its effectiveness for subsequent use as a drivable fastening device, not only because it was essentially permanently embedded in the penetrated work material, but also because the initially sharp point on the tip of the stud was blunted. Moreover, studs of the type shown in said Cox patent were not provided at their head end with centering surfaces adapted to mate with corresponding surfaces of the hammering piston of a hand-held driving tool, and thus such studs were not satisfactory for the use to which the present invention is directed.

Accordingly, it is an object of this invention to provide improved fastening techniques. A further object of this invention is to provide an improved method for fastening objects to hard material such as concrete and cement. Other objects, aspects and advantages of the invention will in part be pointed out in, and in part apparent from, the following description of a preferred embodiment of the invention, considered together with the accompanying drawings, in which:

FIGURE 1 is a separated perspective view of a studdriving tool including means for fastening objects to hard material in accordance with this invention;

FIGURE 2 is a vertical section through the assembled tool of FIGURE 1;

FIGURE 3 is a detail section showing the stud after it has been driven into the hard material;

FIGURE 4 is an enlarged side view of a stud having a screw-thread head;

FIGURE 5 shows a modified stud used to fasten a relatively thick piece of wood to hard material; and

FIGURE 6 is a chart comprising a graph showing the variation of stud holding strength as a function of shank taper angle.

Referring now to FIGURES 1 and 2, there is shown a stud-driving tool having a tubular guide 10 formed with a cylindrical bore 12 within which is slidably mounted a piston member 14. Detachably secured to the top of piston member 14, by means of a catch device 16, is a driving member 18 which is slidable in a passage 20 and extends out of the upper end of the tool to permit it to be struck by a hand-held hammer. The lower end of the piston member 14 is formed with conical centering surfaces, in this case generally spherical in shape, adapted to mate with corresponding centering surfaces on the head end 22 of a stud 24 positioned vertically within the bore 12. The lower portion of the stud is provided with a washer 26 dimensioned to engage the side walls of bore 12 and guide the forward end of the stud during a driving operation.

The lower end of the tubular guide 10 is formed with a laterally-extending base flange 28 which serves to stabilize the tool, i.e. minimize tilting of the tool, with respect to the hard material against which the flange is pressed. Within the mouth of the bore 12 is a circular lip 30 which protrudes a small distance into the bore, and is dimensioned to engage the washer 26 to prevent the stud from falling out of the tool before the tool is positioned against the hard material.

The stud 24 is driven into the hard material (see FIG- URE 3) by one or more hammer-like impacts applied by the piston member 14, the stud being guided during this operation by the mating centering surfaces at the head end and by the washer 26 at its lower end. The shank of the stud, ie the main portion between the head and the sharply pointed tip, is conically tapered at a very slight angle, preferably about 15 as measured from one side of the shank to the opposite side. The stud is tapered inwardly towards the tip, that is, the crosssectional area near the tip is smaller than that near the head end. With such an arrangement, it has been found that the stud, after having been driven into hard material such as concrete and cement, will have a holding power, or pull-out strength, markedly superior to fastenings accomplished by conventional techniques.

FIGURE 4 shows a modified steel stud 32 which also is suitable for use in fastening in accordance with the present invention. The head end of this stud is formed with a turned thread 33 and conical centering surfaces 34 adapted to mate with corresponding, e.g. congruent, centering surfaces 36 in a piston member 14a. The short tip 38 of the stud has a sharp penetrating point 40. The elongated shank 42 of the stud is conically tapered at a slight angle, preferably about 1.5" as measured between opposite sides of the shank.

FIGURE 5 shows another stud adapted particularly for fastening relatively thick objects, such as wooden strips, to concrete. The lower portion 44 of the stud shank, i.e. the portion embedded in the concrete, is tapered at an included angle of 1.5 while the upper shank portion 46 (in the wood) is cylindrical. The head 48 of this stud is formed with centering surfaces arranged to mate with corresponding centering surfaces of a piston member (not shown). The tip of the stud is formed with a sharp penetrating point 50 to insure smooth penetration of the concrete.

FIGURE 6 is a graph illustrating the improvement in holding power achieved by fastening in accordance with the present invention. This graph comprises a curve 52 representing the holding power of studs driven into concrete as described above (the holding power being measured in pounds of force required to pull the stud out of the concrete) plotted against the conical taper angle of the stud shank between zero and 7. Points defining the basic test data also are indicated on the graph, each such point representing the average holding power of a group of 50 test studs having identical taper angles. The concerte into which the test studs were driven had a very fine granulated structure and a hardness of about 3650 psi. Within any group of 50 test studs there were small variations in the holding power of individual fastenings, attributable to local inhomogeneity of the concrete; the average holding power for each group of studs was determined by the method of least squares.

The graph of FIGURE 6 indicates that the holding power of a fastening made in accordance with this invention is maximum when the stud shank is tapered at an angle of 1.5 as measured between opposite sides of the shank. At this maximum point, the holding power is very nearly double the holding power of a fastening made with a stud having a cylindrical shank (zero degrees), and approximately three times that of a fastening made with a stud tapered at an angle of about 7 as in the abovementioned prior patent to Cox. It will also be apparent that the improvement achieved by the present invention is obtainable by using studs with taper angles within a small range about 1.5, for example, a stud having an included taper angle of 3 can be expected to provide a holding power of approximately of maximum, and considerably higher than either a cylindrical stud or a stud having a taper angle of 7.

Although several specific embodiments of the invention have been set forth in detail, it is desired to emphasize that these are not intended to be exhaustive or necessarily limitative; on the contrary, the showing herein is for the purpose of illustrating the invention and thus to enable others skilled in the art to adapt the invention in such ways as meet the requirements of particular applications, it being understood that various modifications may be made without departing from the scope of the invention as limited by the prior art.

I claim:

The method of fastening objects to friable hard material comprising the steps of positioning a drive fastener with a sharp penetrating point adjacent the hard material and with the shank of the fastener tapered inwardly towards the tip at an included angle of about 1.5"; driving the fastener into the hard material by substantial force applied suddenly to the head end of the fastener through a piston member having substantial weight relative to the weight of the fastener and with relatively low speed of penetration; guiding said fastener in the region thereof directly above said hard material during the entire driving operation by the contact therewith of means having an axial dimension small relative to the length of said shank and freely shiftable longitudinally along said shank while the fastener is being driven in; accurately guiding said fastener at the head end thereof during the entire driving operation by the contact of centering surfaces with corresponding mating centering surfaces on the head end of said fastener; and maintaining said fastener perpendicular to the surface of the hard material by supporting said guiding means and said piston member with an encircling structure having a stabilizing member at the end thereof in engagement with said hard material during the entire driving operation, whereby the holding power of the fastener is substantially increased.

References Cited UNITED STATES PATENTS 535,503 3/1895 Kornder 227147 2,576,473 11/ 1951 Meyers 29432 2,666,252 1/1954 Temple 29432 2,722,004 11/1955 Webber et al. 29-432 2,724,116 11/1955 Termet 227-9 2,896,209 11/1959 Hilti 227-147 JOHN F. CAMPBELL, Primary Examiner.

THOMAS H. EAGER, Examiner, 

